The invention relates to a gear assembly comprising two strain wave gears. The double strain wave gear arrangement, which is referred herein as dual strain wave gearing enables the connect of a motor to a gear assembly according to the invention to produce a compact gear motor organization. One advantageous application of such a motor is in mechanism characterized by a high torsional moment, a low speed of rotation, a small availability of space and low weight and where good parking accuracy may be required from the power device. An example of such device is the driving means of the movement joints in industrial robots.
In several known motor types, the greatest power is obtained from the motor at a speed of rotation higher than what is required for moving the load. Therefore, a reduction gear must be provided between the motor and the load so that the greater power obtained from the motor can be utilized as a high torsional moment at a low speed of rotation. As is known, a strain wave or harmonic gear provides a high reduction ratio while the gear takes up little space and its performance is good.
The principle of a strain wave gear is disclosed in U.S. Pat. No. 2,906,143, Sept. 29, 1959, Musser, and that of a dual strain wave gear in U.S. Pat. No. 2,943,513, Jun. 5,1960, Musser.